I just found the termination email in the "all mail" folder in my gmail account.
They cite Section 22.d of the member agreement, which says:
"d. Suspension of Use; Cancellation; Closure
We, in our sole discretion, may limit your use of, suspend or terminate your privileges with respect to, your Account, Family Account(s), SetAside Account, Walmart Buck$ balance and/or Card or any feature or benefit thereof, with or without cause or notice, other than any notice required by Applicable Law, including in the event we believe there has been a breach in security or there has been unauthorized activity involving your Account or you have engaged in activity that is fraudulent or inappropriate or that violates the terms of this Member Agreement. We reserve the right to suspend or close your Account (or Family Account(s), SetAside Account or Walmart Buck$ balance) if, among other reasons, (i) you neither Add Funds to nor use your Account, Family Account, SetAside Account and/or Card for extended periods, (ii) there are no funds remaining in your Account or Family Account or SetAside Account for extended periods, (iii) you attempt to Add Funds to your card from an Add Funds Source and are declined or dishonored repeatedly, (iv)you structure purchases or conduct transactions with your Account, Family Account, SetAside Account and/or Card to manufacture spend, (v) you withdraw your consent to deal with us electronically pursuant to the Consent Statement or (vi) for any other reason permitted by Applicable Law. We may, in our sole discretion, decide not to immediately exercise our rights pursuant to this paragraph, but such forbearance (whether once or repeatedly) shall not constitute a waiver nor shall it preclude our right to exercise our rights in the future. "